Modulated pulsed ultrasonic power delivery system and method

ABSTRACT

A method and apparatus for delivering energy during a surgical procedure such as phacoemulsification is provided. The method and apparatus include applying energy during at least one pulsed energy on period, typically sufficient or intended to rapidly induce and beneficially employ transient cavitation. Applying energy during the pulsed energy on period comprises applying energy during a first high energy period, and applying energy during a second nonzero lower energy period.

This application is a divisional of co-pending U.S. patent applicationSer. No. 13/200,061, filed on Sep. 16, 2011, which is a divisional ofco-pending U.S. patent application Ser. No. 12/005,865, filed on Dec.28, 2007, now U.S. Pat. No. 8,020,565, which is a continuation of U.S.patent application Ser. No. 10/387,335, filed on Mar. 12, 2003, now U.S.Pat. No. 7,316,664, which is a continuation-in-part of U.S. patentapplication Ser. No. 10/278,775, filed on Oct. 21, 2002, now U.S. Pat.No. 7,077,820, all of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of surgical tissueremoval systems, and more specifically to modulated pulsed ultrasonicpower delivery during surgical procedures such as phacoemulsification.

2. Description of the Related Art

Phacoemulsification surgery has been successfully employed in thetreatment of certain ocular problems, such as cataracts.Phacoemulsification surgery utilizes a small corneal incision to insertthe tip of at least one phacoemulsification handheld surgical implement,or handpiece. The handpiece includes a needle which is ultrasonicallydriven once placed within an incision to emulsify the eye lens, or breakthe cataract into small pieces. The broken cataract pieces maysubsequently be removed using the same handpiece or another handpiece ina controlled manner. The surgeon may then insert lens implants in theeye through the incision. The incision is allowed to heal, and theresults for the patient are typically significantly improved eyesight.

As may be appreciated, the flow of fluid to and from a patient through afluid infusion or extraction system and power control of thephacoemulsification handpiece is critical to the procedure performed.Different medically recognized techniques have been utilized for thelens removal portion of the surgery. Among these, one popular techniqueis a simultaneous combination of phacoemulsification, irrigation andaspiration using a single handpiece. This method includes making theincision, inserting the handheld surgical implement to emulsify thecataract or eye lens. Simultaneously with this emulsification, thehandpiece provides a fluid for irrigation of the emulsified lens and avacuum for aspiration of the emulsified lens and inserted fluids.

Currently available phacoemulsification systems include a variable speedperistaltic pump, a vacuum sensor, an adjustable source of ultrasonicpower, and a programmable microprocessor with operator-selected presetsfor controlling aspiration rate, vacuum and ultrasonic power levels. Aphacoemulsification handpiece is interconnected with a control consoleby an electric cable for powering and controlling the piezoelectrictransducer. Tubing provides irrigation fluid to the eye and enableswithdrawal of aspiration fluid from an eye through the handpiece. Thehollow needle of the handpiece may typically be driven or excited alongits longitudinal axis by the piezoelectric effect in crystals created byan AC voltage applied thereto. The motion of the driven crystal isamplified by a mechanically resonant system within the handpiece suchthat the motion of the needle connected thereto is directly dependentupon the frequency at which the crystal is driven, with a maximum motionoccurring at a resonant frequency. The resonant frequency is dependentin part upon the mass of the needle interconnected therewith, which istypically vibrated by the crystal.

A typical range of frequency used for phacoemulsification handpiece isbetween about 25 kHz to about 50 kHz. A frequency window exists for eachphacoemulsification handpiece that can be characterized by specifichandpiece impedance and phase. The aforementioned frequency window isbounded by an upper frequency and a lower cutoff frequency. The centerof this window is typically the point where the handpiece electricalphase reaches a maximum value.

Handpiece power transfer efficiency is given by the formula (V*I)(COSΦ), where Φ is the phase angle. Using this power transfer efficiencyequation, the most efficient handpiece operating point occurs when thephase is closest to 0 degrees. Thus optimum handpiece power transferefficiency requires controlling power frequency to achieve a phase valueas close to zero degrees as possible. Achieving this goal is complicatedby the fact that the phase angle of the ultrasonic handpiece alsodepends on transducer loading. Transducer loading occurs through themechanically resonant handpiece system, including the needle. Contact bythe needle with tissue and fluids within the eye create a load on thepiezoelectric crystals with concomitant change in the operating phaseangle.

Consequently, phase angles are determined and measured at all timesduring operation of the handpiece to adjust the driving circuitry,achieve an optimum phase angle, and effect constant energy transfer intothe tissue by the phacoemulsification handpiece. Automatic tuning of thehandpiece may be provided by monitoring the handpiece electrical signalsand adjusting the frequency to maintain consistency with selectedparameters. Control circuitry for a phacoemulsification handpiece caninclude circuitry for measuring the phase between the voltage and thecurrent, typically identified as a phase detector. Difficulties mayarise if phase shift is measured independent of the operating frequencyof the phacoemulsification handpiece, because phase shift depends onhandpiece operating frequency, and time delay in the measurement thereofrequires complex calibration circuitry to provide for responsive tuningof the handpiece.

Power control of the phacoemulsification handpiece is highly critical tosuccessful phacoemulsification surgery. Certain previous systems addressthe requirements of power control for a phacoemulsification handpiecebased on the phase angle between voltage applied to a handpiecepiezoelectric transducer and the current drawn by the piezoelectrictransducer and/or the amplitude of power pulses provided to thehandpiece. The typical arrangement is tuned for the particularhandpiece, and power is applied in a continuous fashion or series ofsolid bursts subject to the control of the surgeon/operator. Forexample, the system may apply power for 150 ms, then cease power for 350ms, and repeat this on/off sequence for the necessary duration of powerapplication. In this example, power is applied through the piezoelectriccrystals of the phacoemulsification handpiece to the needle causingultrasonic power emission for 150 ms, followed by ceasing application ofpower using the crystals, handpiece, and needle for 350 ms. It isunderstood that while power in this example is applied for 150 ms, thisapplication of power includes application of a sinusoidal waveform tothe piezoelectric crystals at a frequesncy of generally between about 25kHz and 50 kHz and is thus not truly “constant.” Application of powerduring this 150 ms period is defined as a constant application of a 25kHz to 50 kHz sinusoid. In certain circumstances, the surgeon/operatormay wish to apply these power bursts for a duration of time, ceaseapplication of power, then reapply at this or another power setting. Thefrequency and duration of the burst is typically controllable, as is thelength of the stream of bursts applied to the affected area. The timeperiod where power is not applied enable cavitation in the affected areawhereby broken sections may be removed using aspiration provided by thehandpiece or an aspiration apparatus.

Additionally, the surgeon operator may wish to employ certain knownprocedures, such as a “sculpt” procedure to break the lens, or a “chop”procedure to collect the nucleus and maintain a strong hold on thebroken pieces. These specialized “chop or quadrant removal” procedurestypically entail applying power or energy in a constant span of anywherefrom approximately 50 milliseconds to 200 milliseconds in duration.

The on/off application of power facilitates breaking the cataract intopieces and relatively efficient removal thereof The ultrasonicallydriven needle in a phacoemulsification handpiece becomes warm duringuse, resulting from frictional heat due in part to mechanical motion ofthe phacoemulsification handpiece tip. In certain circumstances, it hasbeen found that the aforementioned method of applying power to theaffected region in a continuous mode can produce a not insignificantamount of heat in the affected area. Irrigation/aspiration fluidspassing through the needle may be used to dissipate this heat, but caremust be taken to avoid overheating of eye tissue duringphacoemulsification, and in certain procedures fluid circulation may notdissipate enough heat. The risk of damaging the affected area viaapplication of heat can be a considerable negative side effect.

Further, the application of power in the aforementioned manner can incertain circumstances cause turbulence and/or chatter, as well as causesignificant flow issues, such as requiring considerable use of fluid torelieve the area and remove particles. Also, the application of constantgroups of energy can cause nuclear fragments to be pushed away from thetip of the handpiece because of the resultant cavitation from the energyapplied. Collecting and disposing of fragments in such a cavitationenvironment can be difficult in many circumstances. These resultanteffects are undesirable and to the extent possible should be minimized.

One system that has been effectively employed in this environment isdisclosed in U.S. patent application Ser. No. 10/278,775, inventorsKadziauskas et al, filed Oct. 21, 2002 and assigned to Advanced MedicalOptics, Inc., the assignee of the present application. The '775application provides for ultrasonic power delivery using relativelybrief applications of power interspersed by short pauses over a longperiod, each long period of power application followed by a lengthy restperiod. This design enables application of energy without the heatproblems associated with previous constant applications of power.

Certain developments have demonstrated that beneficial effects beyondthose demonstrated in the design of the '775 application may be obtainedby employing those beneficial effects associated with cavitation in theenvironment described. Certain types of cavitation can provide forimproved occlusion breakup in some conditions. Understanding andemploying the beneficial effects of cavitation may thus provide forenhanced removal of the nucleus in a phacoemulsification procedurewithout the heat associated with the previous designs.

Based on the foregoing, it would be advantageous to provide a systemthat employs those benefits associated with cavitation and minimizesthose drawbacks associated with previous tissue removal systems.

SUMMARY OF THE INVENTION

According to one aspect of the present design, there is presented amethod for delivering energy during a surgical procedure, comprisingapplying energy during a modulated energy delivery period. The modulatedenergy delivery period comprises applying energy during a plurality ofshort burst periods, the short burst periods comprising a high energyburst period followed a predetermined time thereafter by a nonzero lowenergy burst period.

These and other objects and advantages of all aspects of the presentinvention will become apparent to those skilled in the art after havingread the following detailed disclosure of the preferred embodimentsillustrated in the following drawings.

DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings in which:

FIG. 1 is a functional block diagram of a phacoemulsification system inaccordance with an aspect of the present invention;

FIG. 2 is a functional block diagram of an alternative aspect of aphacoemulsification system including apparatus for providing irrigationfluid at more than one pressure to a handpiece;

FIG. 3 is a flow chart illustrating the operation Of theoccluded-unoccluded mode of the phacoemulsification system with variableaspiration rates;

FIG. 4 is a flow chart illustrating the operation Of theoccluded-unoccluded mode of the phacoemulsification system with variableultrasonic power levels;

FIG. 5 is a flow chart illustrating the operation of a variable dutycycle pulse function of the phacoemulsification system;

FIG. 6 is a flow chart illustrating the operation of theoccluded-unoccluded mode of the phacoemulsification system with variableirrigation rates;

FIG. 7 is a plot of the 90 degree phase shift between the sine waverepresentation of the voltage applied to a piezoelectricphacoemulsification handpiece and the resultant current into thehandpiece;

FIG. 8 is a plot of the phase relationship and the impedance of atypical piezoelectric phacoemulsification handpiece;

FIG. 9 is a block diagram of improved phase detector circuitry suitablefor performing a method in accordance with the present invention;

FIG. 10 is a plot of phase relationship as a function of frequency forvarious handpiece/needle loading;

FIG. 11 is a function block diagram of a phase controlphacoemulsification system utilizing phase angles to controlhandpiece/needle parameters with max phase mode operation;

FIG. 12 is a function block control diagram of a phase controlphacoemulsification system utilizing phase angles to controlhandpiece/needle parameters with a load detect method;

FIG. 13 is a function block control diagram of a pulse controlphacoemulsification system;

FIG. 14 illustrates different ultrasonic energy pulse characteristicsfor pulses provided by the power level controller and computer via thehandpiece;

FIG. 15 is a plot of signal strength for a system applying continuousenergy in a fluid under different level power settings;

FIG. 16 shows signal strength after noise floor removal and onlycavitation excursions plotted for a system applying continuous energy ina fluid under different level power settings;

FIG. 17 illustrates performance of a system employing periodic powerapplication settings;

FIG. 18 compares signal strength for continuous operation againstperiodic power application;

FIG. 19 shows a comparison between continuous operation signal strengthand periodic microburst energy application signal strength;

FIG. 20 illustrates relative cavitation energy over time for variousenergy application settings;

FIG. 21 shows a waveform according to the present design;

FIGS. 22A through 22I show alternate examples of waveforms according tothe present design;

FIG. 23 presents a conceptual block diagram of computation and deliveryof the enhanced ultrasonic energy waveform of the present invention; and

FIGS. 24A and 24B illustrate waveforms provided in the presence of anocclusion or other sensed change in flow, pressure, or vacuumconditions.

DETAILED DESCRIPTION OF THE INVENTION

Device.

FIG. 1 illustrates a phacoemulsification system in block diagram form,indicated generally by the reference numeral 10. The system has acontrol unit 12, indicated by the dashed lines in FIG. 1 which includesa variable speed peristaltic pump 14, which provides a vacuum source, asource of pulsed ultrasonic power 16, and a microprocessor computer 18that provides control outputs to pump speed controller 20 and ultrasonicpower level controller 22. A vacuum sensor 24 provides an input tocomputer 18 representing the vacuum level on the input side ofperistaltic pump 14. Suitable venting is provided by vent 26.

A phase detector 28 provides an input to computer 18 representing aphase shift between a sine wave representation of the voltage applied toa handpiece/needle 30 and the resultant current into the handpiece 30.The block representation of the handpiece 30 includes a needle andelectrical means, typically a piezoelectric crystal, for ultrasonicallyvibrating the needle. The control unit 12 supplies power on line 32 to aphacoemulsification handpiece/needle 30. An irrigation fluid source 34is fluidly coupled to handpiece/needle 30 through line 36. Theirrigation fluid and ultrasonic power are applied by handpiece/needle 30to a patient's eye, or affected area or region, indicateddiagrammatically by block 38. Alternatively, the irrigation source maybe routed to the eye 38 through a separate pathway independent of thehandpiece. The eye 38 is aspirated by the control unit peristaltic pump14 through line/handpiece needle 40 and line 42. A switch 43 disposed onthe handpiece 30 may be utilized as a means for enabling asurgeon/operator to select an amplitude of electrical pulses to thehandpiece via the computer 18, power level controller 22 and ultrasonicpower source 16 as discussed herein. Any suitable input means, such as,for example, a foot pedal (not shown) may be utilized in lieu of theswitch 43.

FIG. 2 shows an alternative phacoemulsification system 50 incorporatingall of the elements of the system 10 shown in FIG. 1, with identicalreference characters identifying components, as shown in FIG. 1. Inaddition to the irrigation fluid source 34, a second irrigation fluidsource 35 is provided with the sources 34, 35 being connected to theline 36 entering the handpiece/needle 30 through lines 34 a, 35 a,respectively, and to a valve 59. The valve 59 functions to alternativelyconnect line 34A and source 34 and line 35A and source 35 with thehandpiece/needle 30 in response to a signal from the power levelcontroller 22 through a line 52.

As shown, irrigation fluid sources 34, 35 are disposed at differentheights above the handpiece/needle 30 providing a means for introducingirrigation fluid to the handpiece at a plurality of pressures, the headof the fluid in the container 35 being greater than the head of fluid inthe container 34. A harness 49, including lines of different lengths 44,46, when connected to the support 48, provides a means for disposing thecontainers 34, 35 at different heights over the handpiece/needle 30.

The use of containers for irrigation fluids at the various heights isrepresentative of the means for providing irrigation fluids at differentpressures, and alternatively, separate pumps may be provided with, forexample, separate circulation loops (not shown). Such containers andpumps can provide irrigation fluid at discrete pressures to thehandpiece/needle 30 upon a command from the power controller 22.

Operation.

The computer 18 responds to preset vacuum levels in input line 47 toperistaltic pump 14 by means of signals from the previously mentionedvacuum sensor 24. Operation of the control unit in response to theoccluded-unoccluded condition of handpiece 30 is shown in the flowdiagram of FIG. 3. As shown in FIG. 3, if the handpiece aspiration line40 becomes occluded, the vacuum level sensed by vacuum sensor 24 mayincrease. The computer 18 may provide operator-settable limits foraspiration rates, vacuum levels and ultrasonic power levels. Asillustrated in FIG. 3, when the vacuum level sensed by vacuum sensor 24reaches a predetermined level as a result of occlusion of the handpieceaspiration line 40, computer 18 provides signals to pump speedcontroller 20 to change the speed of the peristaltic pump 14 which, inturn, changes the aspiration rate. Depending upon the characteristics ofthe material occluding handpiece/needle 30, the speed of the peristalticpump 14 can either be increased or decreased. When the occludingmaterial is broken up, the vacuum sensor 24 registers a drop in vacuumlevel, causing computer 18 to change the speed of peristaltic pump 14 toan unoccluded operating speed.

In addition to changing the phacoemulsification parameter of aspirationrate by varying the speed of the peristaltic pump 14, the power level ofthe ultrasonic power source 16 can be varied as a function of theoccluded or unoccluded condition of handpiece 30. FIG. 4 illustrates inflow diagram form a basic form of control of the ultrasonic power sourcepower level using computer 18 and power level controller 22. The flowdiagram of FIG. 4 corresponds to the flow diagram of FIG. 3 but variesthe phacoemulsification parameter of the ultrasonic power level.

The impedance of the typical phacoemulsification handpiece varies withfrequency, or in other words, the handpiece is reactive. Dependence oftypical handpiece phase and impedance as a function of frequency isshown in FIG. 8. In FIG. 8, curve 64 represents the phase differencebetween current and voltage of the handpiece as function frequency andcurve 66 shows the change in impedance of the handpiece as a function offrequency. The impedance exhibits a low at “Fr” and a high “Fa” for atypical range of frequencies, such as in the range of approximately 25kHz to approximately 50 kHz.

Automatic tuning of the handpiece typically requires monitoring thehandpiece electrical signals and adjusting the frequency to maintain aconsistency with selected parameters. To compensate for a load occurringat the tip of the phacoemulsification handpiece, the drive voltage tothe handpiece can be increased while the load is detected and thendecreased when the load is removed. This phase detector is typicallypart of the controller in this type of system. In such conventionalphase detectors, the typical output is a voltage as proportional to thedifference in alignment of the voltage and the current waveform, forexample, −90 degrees as shown in FIG. 7. As shown in FIG. 8, while usingthe handpiece, the waveform varies in phase and correspondingly theoutput waveform also varies.

Heretofore, the standard technique for measuring electrical phase hasbeen to read a voltage proportional to phase and also to frequency. Thistype of circuit may be calibrated for use with a single frequency.Changing the frequency may cause the calibration data to be incorrect.As also seen in single frequency systems, corrected phase value willdrift due to variation in the circuit parameters.

One other available approach utilizes a microprocessor to compare thevalue of the phase detector output with that of a frequency detector andcompute the true phase. This approach is fairly complex and is subjectto drift of the individual circuits as well as resolution limitations. Ablock diagram 70 as shown in FIG. 9 is representative of an improvedphase detector suitable for performing in accordance with the design.Each of the function blocks shown comprises conventionalstate-of-the-art circuitry of typical design and components forproducing the function represented by each block as hereinafterdescribed.

The system converts voltage input 72 and current 74 from aphacoemulsification handpiece 30 to an appropriate signal using anattenuator 76 on the voltage signal to the phacoemulsificationhandpiece, and a current sense resistor 78 and fixed gain amplifier forthe handpiece 30 current. Thereafter, the system passes an AC voltagesignal 80 and AC current signal 82 to comparators 84, 86 which convertthe analog representations of the phacoemulsification voltage andcurrent to logic level clock signals.

The system feeds output from the comparator 84 into a D flip flopintegrated circuit 90 configured as a frequency divide by 2. The systemthen feeds output 92 of the integrated circuit 90 into an operationalamplifier configured as an integrator 94. The output 96 of theintegrator 94 is a sawtooth waveform of which the final amplitude isinversely proportional to the handpiece frequency. A timing generator 98uses a clock synchronous with the voltage signal to generate A/Dconverter timing, as well as timing to reset the integrators at the endof each cycle. The system feeds this signal into the voltage referenceof an A/D converter via line 96.

The voltage leading edge to current trailing edge detector 100 uses a Dflip flop integrated circuit to isolate the leading edge of thehandpiece voltage signal. This signal is used as the initiation signalto start the timing process between the handpiece 30 voltage andhandpiece 30 current. The output 102 of the leading edge to currenttrailing edge detector 100 is a pulse proportional to the timedifference in occurrence of the leading edge of the handpiece 30 voltagewaveform and the falling edge of the handpiece current waveform.

The system uses another integrator circuit 104 for the handpiece phasesignal 102 taken from the leading edge to current trailing edge detector100. Output 106 of the integrator circuit 104 is a sawtooth waveform inwhich the peak amplitude is proportional to the time difference in theonset of leading edge of the phacoemulsification voltage and thetrailing edge of the onset of the handpiece current waveform. The systemfeeds output 106 of the integrator circuit 104 into the analog input oran A/D (analog to digital converter) integrated circuit 110. Thepositive reference input 96 to the A/D converter 110 is a voltage thatis inversely proportional to the frequency of operation. The phasevoltage signal 96 is proportional to the phase difference between theleading edge of the voltage onset, and the trailing edge of the currentonset, as well as inversely proportional to the frequency of operation.In this configuration, the two signals frequency voltage reference 96and phase voltage 106 track each other over the range of frequencies, sothat the output of the A/D converter 110 produces the phase independentof the frequency of operation.

In this arrangement, the system computer 18 (see FIGS. 1 and 2) isprovided with a real time digital phase signal wherein 0 to 255 countswill consistently represent 0 to 359 degrees of phase. No form ofcalibration is necessary since the measurements are consistent despitethe frequencies utilized. For example, using AMPs operation frequenciesof 38 kHz and 47 kHz and integrator having a rise time of 150×10⁵ V/secand an 8 bit A/D converter having 256 counts, a constant ratio ismaintained and variation in frequency does not affect the results. Thisshown in the following examples.

EXAMPLE 1 38 KHz Operation

Period of 1 clock cycle=1/F @38 KHz=26.32 times 10⁻⁶ S

Portion of one period for I=90 deg=26.32 times 10⁻⁶ S

-   -   Divided by 4=6.59 times 10⁻⁶ S

Integrator output for one reference cycle=(150 times 10³ V/S) times(26.32 times 10⁻⁶ S)=3.95 Volts

Integrator output from 90 degree cycle duration=(150 times 10³ V/S)times (6.59 times 10⁻⁶ S)=0.988 Volts

Resulting Numerical count from A/D converter=3.95 Volts/256counts=0.0154 Volts per count

Actual Number of A/D counts for 90 deg at 38 KHz=0.988/0.0154=64 counts

EXAMPLE 2 47 KHz Operation

Period of 1 clock cycle=1/F @47 KHz=21.28 times 10⁻⁶ S

Portion of one period for I=90 deg=21.28 times 10⁻⁶ S

-   -   Divided by 4=5.32 times 10⁻⁶ S

Integrator output for one reference cycle=(150 times 10³ V/S) times(21.28 times 10⁻⁶ S)=3.19 volts

Integrator output from 90 degree cycle duration=(150 times 10³ V/S)times (5.32 times 10⁻⁶ S)=0.798 Volts

Resulting Numerical count from A/D converter =3.19 Volts/256counts=0.0124 Volts per count

Actual Number of A/D counts for 90 deg at 47 KHz=0.798/0.0124=64 counts

This represents the baseline operation of the present system, namely theability to tune the phacoemulsification handpiece to a generallyacceptable level.

Energy Delivery.

The following sections deal generally with the types of delivery ofmicroburst energy generally employed to effectively carry out thephacoemulsification procedure. With reference to FIG. 5, there is showna flow diagram depicting basic control of the ultrasonic power source 16to produce varying pulse duty cycles as a function of selected powerlevels. Each power pulse may have a duration of less than 20milliseconds. As shown in FIG. 5, and by way of illustration only, a 33%pulse duty cycle is run until the power level exceeds a presetthreshold; in this case, 33%. At that point, the pulse duty cycle isincreased to 50% until the ultrasonic power level exceeds a 50%threshold, at which point the pulse duty cycle is increased to 66%. Whenthe ultrasonic power level exceeds 66% threshold, the power source isrun continuously, i.e., a 100% duty cycle. Although the percentages of33, 50 and 66 have been illustrated in FIG. 5, it should be understoodthat other percentage levels can be selected as well as various dutycycles to define different duty cycle shift points. The pulse durationin this arrangement may be less than 20 milliseconds. This control alongwith the tracking mechanism herein described enables bursts of energyless than 20 milliseconds in duration.

With reference to FIG. 13, a rapid pulse duration of less than 20milliseconds is provided with adequate energy to cut the tissue withkinetic or mechanical energy. The ultrasonic energy pulse may then beturned off long enough to significantly decrease the resultant heatlevel before the next pulse is activated. A surgeon/operator may varythe pulse amplitude in a linear manner via the switch 143 and thecontrol unit 22 in response to the selected pulse amplitude, irrigationand aspiration fluid flow rates, controlling a pulse duty cycle. Ashereinabove noted, an off duty duration or cycle is provided to ensureheat dissipation before a subsequent pulse is activated. In this way,increased amplitude will increase tip acceleration and thus heatdissipation level for tissue damaging heat generation. That is, thesurgeon/operator can use linear power control to select the correctacceleration necessary to cut through the tissue density while thecontrol unit provides a corresponding variation in pulse width of lessthan 20 milliseconds and “off time” to prevent tissue de-compensationfrom heat. The control unit is programmed depending on thephacoemulsification handpiece chosen (total wattage) or thephacoemulsification tip (dimensions, weight). This use of rapid pulsingis similar to how lasers operate with very short duration pulses. Pulsesin this configuration may have a repetition rate of between about 25 and2000 pulses per second.

With reference to FIG. 5, if the handpiece aspiration line 38 isoccluded, the vacuum level sensed by the vacuum sensor 24 will increase.The computer 18 has operator-settable limits for controlling which ofthe irrigation fluid supplies 32, 33 will be connected to the handpiece30. While two irrigation fluid sources, or containers 32, 33 are shown,any number of containers may be utilized.

As shown in FIG. 6, when the vacuum level by the vacuum sensor 24reaches a predetermined level, as a result of occlusion of theaspiration handpiece line 38, the computer controls the valve 38 causingthe valve to control fluid communication between each of the containers34, 35 and the handpiece/needle 30.

Depending upon the characteristics of the material occluding thehandpiece/needle 30, as hereinabove described and the needs andtechniques of the physician, the pressure of irrigation fluid providedthe handpiece may be increased or decreased. As occluded material iscleared, the vacuum sensor 24 may register a drop in the vacuum levelcausing the valve 38 to switch to a container 34, 35, providing pressureat an unoccluded level.

More than one container may be utilized, such as three containers (notshown) with the valve interconnecting to select irrigation fluid fromany of the three containers, as hereinabove described in connection withthe container system.

In addition to changing phacoemulsification handpiece/needle 30parameter as a function of vacuum, the occluded or unoccluded state ofthe handpiece can be determined based on a change in load sensed by ahandpiece/needle by way of a change in phase shift or shape of the phasecurve. A plot of phase angle as a function of frequency is shown in FIG.10 for various handpiece 30 loading, a no load (max phase), light load,medium load and heavy load.

With reference to FIG. 11, representing max phase mode operation, theactual phase is determined and compared to the max phase. If the actualphase is equal to, or greater than, the max phase, normal aspirationfunction is performed. If the actual phase is less than the max phase,the aspiration rate is changed, with the change being proportionate tothe change in phase. FIG. 12 represents operation at less than max loadin which load (see FIG. 10) detection is incorporated into theoperation.

As represented in FIG. 11, representing max phase mode operation, if thehandpiece aspiration line 40 is occluded, the phase sensed by phasedetector sensor 28 will decrease (see FIG. 10). The computer 18 hasoperator-settable limits for aspiration rates, vacuum levels andultrasonic power levels. As illustrated in FIG. 11, when the phasesensed by phase detector 28 reaches a predetermined level as a result ofocclusion of the handpiece aspiration line 40, computer 18 instructspump speed controller 20 to change the speed of the peristaltic pump 14which, in turn, changes the aspiration rate.

Depending upon the characteristics of the material occludinghandpiece/needle 30, the speed of the peristaltic pump 14 can either beincreased or decreased. When the occluding material is broken up, thephase detector 28 registers an increase in phase angle, causing computer18 to change the speed of peristaltic pump 14 to an unoccluded operatingspeed.

In addition to changing the phacoemulsification parameter of aspirationrate by varying the speed of the peristaltic pump 14, the power leveland/or duty cycle of the ultrasonic power source 16 can be varied as afunction of the occluded or unoccluded condition of handpiece 30 ashereinabove described.

Microburst Enhanced Operation.

A representation of different pulse characteristics for previousoperation is presented in FIG. 14. From FIG. 14, operation of pulses maybe a constant application of power at a frequency of between about 25kHz to about 50 kHz as illustrated in Plot A, or once every 80milliseconds for a duration of 40 milliseconds on and 40 millisecondsoff as in Plot B, representing 12.5 pulses per second. Alternately,ultrasonic power delivery may occur once every 40 ms, for 20 ms on and20 ms off as in Plot C. Plot D shows power applied every 20 ms for 10 msand turned off for 10 ms. Other non periodic arrangements may beemployed, such as shown in Plot E, with application of power for 10 msperiodically every 40 ms, with a resultant 30 ms off time.

These power application intervals represent solid, constant periods whenultrasonic power is being applied to the handpiece and needle at aconstant power level for a period of time. Again, while power may appearin the Figures to be applied at a continuous DC type of application, theFigures are intended to indicate actual application of power including asinusoidal waveform being applied to the piezoelectric crystals at afrequency of generally between about 25 kHz and 50 kHz. The applicationof power is therefore not truly “constant.” Application of power duringthis 150 ms period is defined as a constant application of a 25 kHz to50 kHz sinusoid.

Cavitation.

The present design offers enhancements over the waveforms of FIG. 14 byemploying beneficial effects of cavitation and applying energyaccordingly. Cavitation in the surgical environment may be defined asthe violent collapse of minute bubbles in fluid, such as saline, water,or other applicable fluid. Cavitation is the primary means by whichcells and nuclei can be broken or cut in ultrasonic surgical systems,including phacoemulsifiers. The system presented above can generatecavitation by providing a series of acoustic pressure waves forming anacoustic pressure field emanating from the tip of the phacoemulsifierhandpiece 30. Acoustic pressure waves are the result of the phaco tiposcillating forward and back at the operating frequency, such as at thefrequency of approximately 38 kHz.

Cavitation is the generation, oscillation, and collapse of minutebubbles in the operating fluid. In a phacoemulsification or othersurgical scenario, bubbles are created by the acoustic waves emanatingfrom the surgical ultrasonic tip, and may therefore be called acousticcavitation. The violent collapse of these bubbles may create most of theforces that break up nuclei or produce the cutting or choppingcharacteristics of tissue fragmentation. Other bubble motion under theinfluence of the pressure field, such as resonant vibration discussedbelow, may also yield a desirable biological effect.

In this ultrasonic environment, acoustic pressure is proportional to theacoustic source strength Qs or volume velocity of the tip, which is theeffective tip area A (typically an annulus) multiplied by tip velocity.Tip velocity is the product of the tip vibration amplitude δ and 2πmultiplied by operating frequency. The tip is relatively small incomparison to the acoustic wavelength in fluid and acts as a pointradiator of sound or monopole source at the operating frequency.

In this environment, low frequency sound tends to radiate in a sphericalmanner, with a pressure level that falls inversely with distance fromthe tip. The pressure field at a distance r from a monopole sourcepulsating at a frequency ω*(2ρf) is given by:

$\begin{matrix}{p = {\left( \frac{{j\rho}_{0}{ck}}{4\; \pi} \right)\left( Q_{s} \right)\frac{^{{- j}\; {kr}}}{r}}} & (1)\end{matrix}$

where ρ_(o) and c are the density and sound speed of the medium, k isthe wave number, or ω/c, and Q_(s) is the source strength. UsingEquation (1), pressure can be expressed as:

$\begin{matrix}{p = \frac{j\; p_{0}\omega^{2}A\; \delta \; ^{{- j}\; k\; r}}{4\; \pi \; r}} & (2)\end{matrix}$

From Equation (2), pressure is related to tip area, displacement, andthe square of the operating frequency. Equation (2) provides a generalguideline for determining pressure equivalence between tips of differentsizes, frequencies, and displacements.

Acoustic source strength Q_(s) may be calculated as follows. Assuming asolid circular, flat end tip, operating at 24,500 Hz, with a radius of1.44 mm, and a vibration amplitude of 100 μm (tip excursion 200 μm):

$\begin{matrix}\begin{matrix}{Q_{s} = {{Area}*{velocity}}} \\{= {\left( {\pi \; r^{2}} \right)*\omega*\delta}} \\{= {\pi*({.00144})^{2}*\left( {2*\pi*24,500} \right)*\left( {100*10^{- 6}} \right)}} \\{Q_{s} = {100 \times 10^{- 6}\mspace{14mu} {meters}^{3}\text{/}{second}}}\end{matrix} & (3)\end{matrix}$

Total acoustic power in this example, W, may be calculated as follows:

$\begin{matrix}{{W = {\rho_{0} \times c \times k^{2} \times {\left( Q_{s} \right)^{2}/8}\pi}}{{where}\text{:}}} & (4) \\{\begin{matrix}{k = {\omega/c}} \\{= {\left( {2*\pi*f} \right)/c}} \\{= {{2*\pi*24,{500/\left. 1500 \right.\sim}} = 100}}\end{matrix}\begin{matrix}{W = {1000*1500*100^{2}*{\left( {10*10^{- 6}} \right)^{2}/8}\pi}} \\{\sim {= {6\mspace{14mu} {Acoustic}\mspace{14mu} {Watts}}}}\end{matrix}} & (5)\end{matrix}$

As the sound passes through fluid, such as water, saline, or otherliquid, the sound encounters microscopic bubbles. A bubble exposed tothe “tensile” or “rarefactional” or “negative” part of the wave has atendency to expand. A bubble exposed to the “compressional” or“positive” portion of the wave tends to decrease in size or shrinkslightly. Gas diffuses into the bubble when in the enlarged state due toforce differences. Gas tends to dissipate, or diffuse out, when thebubble decreases in size. Because the surface area of the decreasedbubble is less than the surface area of the enlarged bubble, less gastends to diffuse out during this portion of the cycle than diffused induring the “enlarged” portion of the cycle. Over time the bubble tendsto increase in size, a phenomenon known as rectified diffusion. If thepressure variation is not significant, the size difference between theenlarged and shrunken state is not significant enough to provideappreciable net gas inflow.

As bubbles increase in size due to rectified diffusion, these bubblescan attain a size wherein hydrodynamic forces on the bubble, such as gaspressure, surface tension, and so forth, reach dynamic equilibrium orresonance with the applied sound field. In situations of dynamicequilibrium, a bubble can oscillate vigorously, collapse and breakapart. This oscillation and collapse of the bubble occurs when thepressure is significant. In the event the pressure is enough to producerectified diffusion, small bubbles will have a tendency to continuouslyincrease in size, oscillate, and then collapse. Bubbles may also dividewithout full collapse, resulting smaller bubbles that increase in sizeand continue the process. This phenomenon may be referred to as stablecavitation.

Stable cavitation produces a collection or cloud of bubbles that tend tooperate in a relatively stable manner as long as the pressure fieldexists. In stable cavitation, many of the bubbles break apart without afull, violent collapse. Inducing stable cavitation may not be wellsuited to cell and nucleus cutting.

Transient cavitation may be defined as violent bubble collapse. Whenbubbles violently collapse near a boundary, such as a cell wall, thebubbles expend a significant amount of pressure on the cell wall. Theeffect is similar to a water hammer producing very high pressures andtemperatures concentrated within a small area. These high pressure/hightemperature conditions can destroy tissue and denature the proteins inthe cell. Transient cavitation results from quick expansion and violentcollapse of bubbles of a very specific size relative to the acousticdriving frequency. This quick expansion and violent collapse resultsfrom the force of the driving waveform. Transient cavitation issensitive to the driving waveform pressure level in that transientcavitation may not occur at all below some threshold level. Above thethreshold, transient cavitation will result as long as bubbles of thecorrect size are available.

The absolute threshold for cavitation phenomena is generally frequencydependent. In generating cavitation, the arrangement described hereintranslates energy from the driving, low frequency ultrasonic waveforminto the mechanical manipulation of bubbles. The driving waveformemanating from the phaco tip may be termed a pumping wave. As morecavitation occurs, more energy is received from the pumping wave. At lowpressure levels, such as below the threshold for cavitation, the lowfrequency pressure emitted from the tip is roughly proportional to tipexcursion. In this low pressure scenario, little pressure is availableto impact the cell wall or nucleus. Some mechanical impact may existsince the phaco tip vibrates and can thus cause frictional heating. Anincrease in driving excursion level tends to increase cavitationactivity.

Further drive amplitude increases result in radiated low frequencypressure no longer having the ability to track amplitude. Thisdecorrelation between pressure and amplitude occurs as a result ofenergy transferring to cavitation. As the drive amplitude is furtherincreased, the low frequency pressure field can decrease. Such adecrease in the pressure field is a result of bubbles obscuring the tipand acting as a cushion shielding the pressure field. This cushion canchange the local acoustical properties of the fluid. Thus the ratio ofpumping energy to cavitational energy changes as drive amplitudeincreases.

FIG. 15 shows the resultant energy applied to a fluid for a systemapplying a constant level of energy, i.e. continuous application ofpower for a period of time, such as 2.0 seconds. The signal 1502 havingmultiple high amplitude spikes is one having a low power setting, whilethe signal 1501 exhibiting lower, choppier characteristic has a higherpower setting. The low power signal 1502 exhibits relatively largesignal excursions, indicative of transient cavitation. Between transientpeaks, the signal level for the low power signal 1502 is atapproximately the noise floor. The choppier and higher power signal 1501exhibits a lower peak level, but a continuous signal above the noisefloor, indicative of stable cavitation.

Removal of the noise floor and plotting of cavitation excursions for thesystem of FIG. 15 is presented in FIG. 16. The two waveforms, high powersignal 1601 and low power signal 1602 display nearly identical overallcavitational energy over the time period shown. Thus while transientcavitation occurs less frequently, transient cavitation tends to releasegreater energy to the region or environment.

FIG. 17 shows the response of a system wherein power is applied inshorter bursts, such as approximately 0.15 milliseconds on followed byapproximately 0.35 milliseconds off The plot of FIG. 17 illustratesperformance after noise thresholding.

The first two bursts 1701 and 1702 begin with significant transientcavitation, but this transient cavitation tends to fall off relativelyrapidly. FIG. 18 shows this long pulsing, 0.15 milliseconds on followedby 0.35 milliseconds off, as compared to continuous application ofpower. The long pulsing signal 1802 and the continuous signal 1801 havesimilar total cavitational energy over the time period, but the pulsedresponse 1802 uses less than approximately half the drive power. Thislower drive power results from the system being energized for less thanapproximately half the time.

FIG. 19 illustrates application of continuous power 1901 in theenvironment and a shorter burst arrangement 1902. This shorter burstperiod 1902 employs a series of bursts such as repeatedly applyingenergy for 6 ms and resting for 24 ms for a total period of 0.2 seconds,then applying de minimis power, such as zero power, for 0.5 seconds.FIG. 19 illustrates that nearly every burst of drive frequency energy inthis shorter burst period 1902 tends to generate transient cavitation.The time between bursts is believed to enable fluid to move sufficientlyto replenish the area with bubbles of sufficient size, or dissolved gas,thus producing an environment again receptive to transient cavitation.

In the present system, based on observation of performance in thepresence of short duration energy delivery, cavitation relates to energydelivery as shown in FIG. 20. FIG. 20 represents various energyapplications in the phacoemulsification environment and the resultantcavitational energy. From FIG. 20, two to three milliseconds aretypically required for the cavitational energy to rise to a maximum. Twoto three milliseconds represents the time required for the phaco tip toachieve the full requested excursion and for the cavitation process,specifically transient cavitation, to commence. Once started, energydelivered tends to fall off, representing the transition from transientto stable cavitation. After six milliseconds, the handpiece becomesde-energized, and only residual “ringing” of the tip producescavitation.

The dashed lines in FIG. 20 represent energy readings taken in thepresence of a continuous application of energy, such as shown in FIGS.15, 16, 18, and 19. From FIG. 20, cavitation energy level issignificantly lower in continuous mode.

Modulated Energy Delivery.

The present design employs stable cavitation and transient cavitation asfollows. Power is applied in brief pulses, with these brief pulseshaving divided energy levels for the phaco environment presented above.In particular, a waveform such as that shown in FIG. 21 may be employed.Other similar waveforms may be employed and depend on the environmentencountered, including but not limited to phaco conditions, tip size,operating frequency, fluid conditions, and occlusion conditions. FIG. 21shows a modulated pulse delivering initial power by an initial energyperiod 2101 at 30 watts for a brief duration, such as 2 ms. The 30 wattsrepresents input to the handpiece. The second period 2102 representspower delivered at 15 watts for a period of 2 ms. The third period 2103represents a time period, in this example three milliseconds, deliveredat a specific level, such as 10 watts. The goal of the modulated orstepped power delivery arrangement is to initiate needle stroke abovethe distance necessary to generate transient cavitation as rapidly aspossible. Once the power threshold required to induce transientcavitation has been achieved, power may be reduced for the remainder ofthe pulse.

As may be appreciated by those skilled in the art, other timing andpower implementations may be employed. Examples of power schemes areprovided in FIGS. 22A-F, where power levels and timing are varied. Thegoal of varying the time and power is to attain transient cavitation asquickly as possible in the environment presented without generatingsignificant heat. FIG. 22A shows a two step modulated pulse at 30 wattsfor 2 ms and 15 watts for 4 ms. FIG. 22B is a 2.5 ms 35 watt pulse,followed by a 1 ms 25 watt pulse, followed by a 1 ms 15 watt pulse,followed by a 1 ms 5 watt pulse. FIG. 22C shows a 25 watt pulse for 2ms, a 15 watt pulse for 0.5 ms, and a 10 watt pulse for 2.5 ms. FIG. 22Dis a 20 watt pulse for 3 ms and a 10 watt pulse for 3 ms. FIG. 22E showsa 40 watt pulse for 1.8 ms, a 25 ms pulse for 2 ms, and a 15 watt pulsefor 3 ms. FIG. 22F is a 30 watt pulse for 3.5 ms, a 25 watt pulse for0.5 ms, a 20 watt pulse for 0.5 ms, a 15 watt pulse for 0.5 ms, and a 10watt pulse for 1 ms. As may be appreciated by one of ordinary skill inthe art, other times and durations may be employed depending oncircumstances.

While FIGS. 22A-F show essentially square waves going on and off atspecific times, it is not essential that the waves be square in nature.FIGS. 22G-I illustrate an alternative aspect of the invention whereinrounded waves, or graduated power delivery curves, are applied to thesurgical area. As shown in FIGS. 22G-I, and as may be appreciated bythose skilled in the art, sufficient power is delivered based on thecircumstances presented to induce transient cavitation, typically bydelivering an initial higher powered surge or burst of energy, followedby a dropoff in energy from the initial surge. The magnitude and time ofthe initial energy surge depends on circumstances presented, and mayexhibit characteristics similar to or based in whole or in part uponcurves similar to those shown in FIG. 20 for a typicalphacoemulsification surgical environment.

The important factor in the present design is to provide transientcavitation in the environment in a relatively brief amount of timefollowed by a permissible dropoff in energy in an attempt to minimizeenergy delivered to the region. Thus a strong or high energy initialpulse followed shortly thereafter or immediately thereafter by at leastone lower power pulse is the critical modulated power delivery method toachieve the foregoing desired performance.

In the environment discussed herein, application of ultrasonic energymay be characterized as a strong or high energy short pulse beingapplied for a short duration followed by a dropoff in ultrasonic energyapplied. Such waveforms include but are not limited to those waveformsshown in FIGS. 22A-22I. Cavitational energy, as represented in FIG. 20,is related to the application of power, but may in fact occur for adifferent time period than the ultrasound energy period. For example,but not by way of limitation, ultrasound energy may be applied forapproximately three milliseconds, reaching a peak during these threemilliseconds, while the resultant cavitational energy may reach a peakat a later time, such as at six milliseconds. Longer or shorter periodsmay be employed and/or observed, and the effectiveness of the differingtime periods depends on the environment wherein the time periods areemployed.

From the foregoing, depending on output conditions, transient or stablecavitation may be generated in different circumstances by the ultrasonicdevice. This cavitation may be employed in varying environments inaddition to those disclosed herein, including but not limited to adiagnostic environment and a chemical processing environment. Thecavitation may also be employed in medical treatments or to enhancemedical treatments. Enhancement of medical treatments may include, forexample, assisting or accelerating the medical treatment. With respectto chemical processing, applying energy in the manner described can havea tendency to minimize heat resulting from ultrasound energytransmission, and can tend to minimize input energy required toeffectuate a given chemical result.

Transient cavitation tends to require certain specific conditions tooccur effectively in the phaco environment, including but not limited tothe availability of properly sized initial bubbles and/or dissolved gasin the fluid. When bubbles of the proper size and/or dissolved gas arenot available, either because of low flow or in the presence of a highoutput level in a continuous power application mode, transientcavitation tends to transition to stable cavitation. Energy present intransient cavitation tends to be higher than that of stable cavitation.Pulsing energy as opposed to constant energy can provide certainadvantages, such as enabling the fluid to resupply properly sizedbubbles to facilitate transient cavitation, consuming and deliveringless total power with less likelihood of causing thermal damage totissue. Further, cavitation in the presence of a pulsed energy deliverymode, for the phaco system described herein, requires approximately twoor three milliseconds to attain a maximum value. Cavitation begins tothen decrease as transient cavitation transitions to stable cavitation.

The pulsing of energy described herein may be performed in software,hardware, firmware, or any combination thereof, or using any device orapparatus known to those skilled in the art when programmed according tothe present discussion. A sample block diagram of the operation of theinvention as may be implemented in software is presented in FIG. 23,which is an extension of the implementation of FIG. 13. From FIG. 23,after evaluating whether pulse mode has been enabled, the systemevaluates whether enhanced pulse mode has been enabled. If not, thesystem proceeds according to FIG. 13.

If enhanced pulse mode has been enabled, the Settings Required arereceived. Settings Required may include, but are not limited to, overallcycle time, a desired procedure or function to be performed (sculpting,chopping, etc.), desire to provide bursts or long continuous periods ofpower application, desired transient cavitation energy applicationamplitude, desired transient cavitation energy application period,desired lower amplitude energy level, desired lower amplitude energyduration, pause between transient application energy bursts, and/orother pertinent information. Certain lookup tables may be provided indetermining Settings Required, including but not limited to tablesassociating popular settings with the specific performance parametersfor the desired setting. For example, if the desired function is “chop,”the system may translate the desired “chop” function selection into astandardized or predetermined set of performance parameters, such as a150 millisecond “burst on” period, followed by an 350 ms “long offperiod,” where the “burst on” period comprises 1 millisecond transientcavitation high energy periods followed by a 3 millisecond lower energyperiod, followed by a 1 millisecond pause, repeated sufficiently to fillthe 150 millisecond “burst on” period. The system takes the SettingsRequired and translates them into an Operation Set, or operation timingset, the Operation Set indicating the desired operation of thephacoemulsification handpiece tip when performing ultrasonic energy orpower delivery.

Input 2302 represents an optional input device, such as a foot pedal,electronic or software switch, switch available on thephacoemulsification handpiece, or other input device known to thoseskilled in the art, that allows the surgeon/operator to engage andenable ultrasonic power to be applied according to the Operation Set.For example, a foot pedal may be supplied that issues an on/off command,such that when depressed power is to be applied according to theoperation set, while when not depressed power is not supplied to thephacoemulsification handpiece tip. Different input devices may enabledifferent modes of operation. For example, a multiple position switchmay be provided that allows for application of ultrasonic poweraccording to one Operation Set, while moving the switch to anotherposition allows for application of ultrasonic power according to adifferent Operation Set. Alternately, one position of the switch mayallow for power application at one level according to one Operation Set,while another position of the switch may enable a higher ultrasonicpower level at the same or a different operational timing set. OperationSet as used herein refers to the timing of pulses and/or energyapplications and on/off periods for the application of power asdescribed herein. Switching may also be nonlinear, such as one detent orsetting for the switch providing only irrigation to the handpiece 30, asecond detent or setting providing a pump on plus irrigation, and athird detent or setting providing irrigation and aspiration whereinultrasound is introduced and may be increased by applying furtherengagement of the switch or foot pedal. In this instance, a foot pedaldepressed to the third position or detent will enable the operator orsurgeon to apply energy according to a base operational timing set andamplitude, such as a first operational timing set with a first transientcavitation inducing amplitude, while further depression of the footpedal would allow application of a second operational timing set and/ora second amplitude. If increased amplitude is desired, depressing thefoot pedal past the third detent may linearly change the amplitude froma value of 0% of available ultrasonic power or tip stroke length to avalue of 100% of ultrasonic power or tip stroke length, or some othervalue between 0% and 100%. In the present design, amplitudes duringenergy application periods typically range from about 0 watts to 35watts at 100% power (input to the handpiece 30).

As may be appreciated, virtually any Operation Set and operation timingset may be employed while within the course and scope of this invention.In particular, the system enables operation in multiple configurationsor operational timing sets, each typically accessible to the user viathe computer. For example, the user may perform a chop operation usingone operational timing set, a sculpt operation using another operationaltiming set, and when encountering particular special conditionsemploying yet another operational timing set. These configurations mayoperate dynamically, or “on the fly.”

The system typically has a frame rate, which may be any period of timeless than the smallest allowable power on or power off period for thedevice. A counter counts the number of pulses, and if the Operation Setdictates that ultrasonic power is to be delivered at a certain framenumber, an indication in the form of an electronic signal is deliveredto the handpiece tip at that frame time. Other implementations beyondthat shown in FIG. 23 may be employed while still within the scope ofthe present invention.

FIG. 24A illustrates the automatic or user controlled altering of theamplitude, with three different amplitude levels having the same timing.Alternate timing may be made available in addition to the differentamplitudes. Additionally, the system may operate to address receipt orencounter of an occlusion as sensed by a sensor, typically located inthe system. As in FIGS. 3 and 4, the handpiece or system may employ asensor to sense a change in flow or vacuum, i.e. pressure, conditions. Achange in flow or vacuum/pressure conditions sensed by the sensorindicates the presence of an occlusion, and upon sensing the presence ofan occlusion, the handpiece or system may feed back an occlusionindication to the computer 18. An occlusion indication may cause thecomputer 18 to automatically alter the Operation Set to an occlusionrelated Operation Set such as that illustrated in FIG. 24B.

It will be appreciated to those of skill in the art that the presentdesign may be applied to other systems that perform tissue extraction,such as other surgical procedures used to remove hard nodules, and isnot restricted to ocular or phacoemulsification procedures. Inparticular, it will be appreciated that any type of hard tissue removal,sculpting, or reshaping may be addressed by the application ofultrasonic power in the enhanced manner described herein.

Although there has been hereinabove described a method and apparatus forcontrolling the ultrasonic power transmitted from a phacoemulsificationhandpiece utilizing, inter alia, the voltage current phase relationshipof the piezoelectric phacoemulsification handpiece and deliveringultrasonic power using relatively short pulses comprising multiple briefpower bursts sufficient to induce transient cavitation in theenvironment presented, for the purpose of illustrating the manner inwhich the invention may be used to advantage, it should be appreciatedthat the invention is not limited thereto. Accordingly, any and allmodifications, variations, or equivalent arrangements which may occur tothose skilled in the art, should be considered to be within the scope ofthe present invention as defined in the appended claims.

What is claimed is:
 1. A method for delivering energy during a surgicalprocedure, comprising: applying energy during a modulated energydelivery period, comprising: applying energy during a plurality of shortburst periods, said short burst periods comprising a high energy burstperiod followed a predetermined time thereafter by a nonzero low energyburst period.
 2. The method of claim 1, wherein the predetermined timeis essentially zero.
 3. The method of claim 1, wherein said short burstperiods further comprise a second nonzero low energy burst period. 4.The method of claim 3, wherein: said nonzero low energy burst periodcomprises a first amplitude; and said second nonzero low energy burstperiod comprises a second amplitude; and said first and second amplitudeare substantially different.
 5. The method of claim 3, wherein saidnonzero low energy burst period comprises a first amplitude; and saidsecond nonzero low energy burst period comprises a second amplitude; andsaid first and second amplitude are substantially equal.
 6. The methodof claim 1, wherein the surgical procedure is performed in a surgicalenvironment, and wherein applying energy during the short burst periodscomprising a high energy burst period followed a predetermined timethereafter by a nonzero low energy burst period tends to inducetransient cavitation in the surgical environment.
 7. The method of claim1, wherein the high energy burst duration is at most approximately fourmilliseconds and said high energy burst induces transient cavitation. 8.The method of claim 1, wherein the high energy burst duration is at mostapproximately two milliseconds and induces transient cavitation.
 9. Asurgical apparatus, comprising: a controller; and a surgical handpiececonfigured to receive commands from a controller and apply modulatedultrasonic energy to a surgical area of a patient in a plurality ofshort burst periods, said short burst periods comprising a relativelyhigh energy burst period followed a predetermined time thereafter by anonzero relatively low energy burst period.
 10. The apparatus of claim9, wherein said surgical handpiece applying modulated ultrasonic energytends to induce transient cavitation within the surgical environment.11. The apparatus of claim 10, wherein said surgical handpiece comprisespiezoelectric crystals configured to deliver ultrasonic energy via thesurgical handpiece in said plurality of short burst periods interspersedby multiple de minimis power application periods.
 12. The apparatus ofclaim 13, wherein said predetermined time is essentially zero.
 13. Theapparatus of claim 13, wherein said surgical handpiece is configured tofurther provide a subsequent nonzero relatively low energy burst period.14. The apparatus of claim 13, wherein said surgical handpiece comprisesa phacoemulsification handpiece having a needle and piezoelectriccrystals configured to provide ultrasonic energy by vibrating saidneedle.
 15. The apparatus of claim 13, further comprising a switchconfigured to enable operation of the apparatus at a first desired timewhen ultrasonic energy application is desired and disable operation ofthe apparatus at a second desired time when ultrasonic energyapplication is not desired.